Compound air and mechanical bearing system and method

Abstract

A bearing system and method may include a first bearing assembly that may have an inner race. An outer race may be disposed around the inner race and may be rotatable relative to the inner race. A second bearing assembly may be disposed around the first bearing assembly. The second bearing assembly may be an air bearing. The outer race may be engageable with the inner race through the engagement mechanism that acts on the outer race so that the inner and outer races rotate together.

What is claimed is: 
     
       1. A bearing system comprising a first bearing assembly that has an inner race and an outer race disposed around the inner race and rotatable relative to the inner race, and a second bearing assembly disposed around the first bearing assembly, the second bearing assembly being an air bearing, and an engagement mechanism wherein the outer race is engageable with the inner race through the engagement mechanism that acts on the outer race by selectively and directly contacting the outer race so that the inner and outer races rotate together, and the engagement mechanism is selectively separable from the outer race releasing the outer race so that the inner and outer races rotate relative to each other. 
     
     
       2. The bearing system according to  claim 1  wherein the first bearing assembly further comprises a number of rolling elements disposed between the inner race and the outer race. 
     
     
       3. The bearing system according to  claim 1  wherein the second bearing assembly includes a foil system and wherein the outer race contacts the foil system at some rotational speeds. 
     
     
       4. The bearing system according to  claim 3  wherein the foil system includes a top foil that contacts the outer race and a bump foil that supports the top foil. 
     
     
       5. The bearing system according to  claim 1  wherein the outer race rotates about a shaft that extends in an axial direction, wherein the engagement mechanism is contained completely within the outer race including in the axial direction. 
     
     
       6. The bearing system according to  claim 5  further comprising a shaft extending through the inner race and wherein the engagement mechanism is an inertial clutch connected to the shaft and includes at least one inertial element that is engageable to contact the outer race. 
     
     
       7. The bearing system according to  claim 1  wherein the engagement mechanism is an electromagnetic clutch and includes an electromagnetic ring. 
     
     
       8. The bearing system according to  claim 1  wherein the engagement mechanism is a clutch and includes a pneumatic actuator. 
     
     
       9. The bearing system according to  claim 1  wherein the outer race rotates about an axis and comprising two sets of rolling elements that are spaced apart along the axis wherein the engagement mechanism is disposed along the axis between the two sets of rolling elements. 
     
     
       10. A bearing system comprising a first bearing assembly that has an inner race and an outer race disposed around the inner race and rotatable relative to the inner race, and a second bearing assembly disposed around the first bearing assembly, the second bearing assembly being an air bearing, and an engagement mechanism wherein the outer race is engageable with the inner race through the engagement mechanism that acts on the outer race so that the inner and outer races rotate together wherein the engagement mechanism is a clutch and includes a pneumatic actuator, and further comprising a compressor wheel rotating with the inner race, wherein the pneumatic actuator is supplied with a pressure from the compressor wheel. 
     
     
       11. A bearing system supporting a shaft for rotation comprising an inner race through which the shaft extends, the inner race rotating with the shaft, an outer race through which the shaft extends and disposed around the inner race and rotatable relative to the inner race, an air bearing assembly that has a foil system disposed around the outer race, the foil system alternatively contacting the outer race or separating from the outer race, and an engagement mechanism that directly contacts the shaft and that selectively contacts the outer race acting thereon so that the outer race rotates with the shaft. 
     
     
       12. The bearing system according to  claim 11  wherein the engagement mechanism comprises a magnetic ring and a friction disc wherein the friction disc is positioned between the magnetic ring and the friction disc so that under select operation of the magnetic ring the friction disc is forced against the outer race. 
     
     
       13. The bearing system according to  claim 11  wherein the engagement mechanism comprises a base fixed directly to the shaft. 
     
     
       14. The bearing system according to  claim 11  wherein the engagement mechanism comprises a pneumatic actuator linked to a pressure plate, with a friction disc positioned between the pressure plate and the outer race. 
     
     
       15. A method comprising providing a shaft operating at variable rotational speed, providing a mechanical bearing assembly selectively supporting the shaft for rotation, providing an air bearing assembly selectively supporting the shaft for rotation, supporting the shaft for rotation with the mechanical bearing assembly during a start-up of the shaft, determining whether the variable rotational speed of the shaft is above a first threshold, when the variable rotational speed is above the first threshold, activating the air bearing assembly, determining one of: a) whether use of the air bearing assembly has an operational efficiency greater than use of the mechanical bearing assembly, or b) whether the variable rotational speed is greater than a bearing loss speed where the bearing loss speed is where a bearing loss is less than a second threshold, and activating the mechanical bearing system if it is determined that either use of the air bearing assembly does not have an operational efficiency greater than use of the mechanical bearing assembly, or the variable rotational speed is greater than a bearing loss speed. 
     
     
       16. The method according to  claim 15  further comprising the step of determining whether the rotational speed is less than the first threshold and activating the mechanical bearing assembly when the rotational speed is less than the first threshold. 
     
     
       17. The method according to  claim 15  further comprising providing a compressor on the shaft that generates a compressor power and determining the bearing loss speed by determining the rotational speeds at which bearing losses are less than five percent of the compressor power. 
     
     
       18. The method according to  claim 15  further comprising activating the mechanical bearing assembly when using the air bearing assembly does not have an operational efficiency greater than using the mechanical bearing assembly. 
     
     
       19. The method according to  claim 15  further comprising providing a pneumatic actuator to activate the air bearing assembly. 
     
     
       20. The method according to  claim 15  further comprising providing an electromagnetic actuator to activate the air bearing system.